The marginal revenue (in thousands of dollars) from the sale of x gadgets is given by the following function. R' (x) = 4x (x2 + 28,000) a. Find the total revenue function if the revenue from 130 gadgets is $23,255. b. How many gadgets must be sold for a revenue of at least $40,000? a. The total revenue function is R(x) = given that the revenue from 130 gadgets is $23,255. (Round to the nearest integer as needed.) b. gadgets must be sold to generate a revenue of at least $40,000. (Type a whole number.)